1. Field of the Invention
This invention relates to dampers for use in heating, ventilating and air conditioning systems where conditioned air is provided from such a system to a plurality of zones, and, more particularly to a damper which provides automatic relief when an excessive duct pressure occurs.
2. Description of the Background Art
In conventional heating, ventilating and air conditioning ("HVAC") systems conditioned air is supplied to a plurality of zones. Zoning systems have been developed for these HVAC systems which typically include dampers disposed in the ductwork for controlling the air flow of the conditioned air to the zones. These zoning systems control the flow of conditioned air to the plurality of zones independently so as to allow for independent control of the zone environments.
However, these zoning systems are difficult and expensive to install, both as original equipment and as retrofit. Implementation of these systems typically requires the installation of dampers in the ductwork, installation of power and control wiring for the components of the system throughout the building, and installation of thermostats in the building walls. Retrofits typically include modifications to the ductwork, power and control wiring throughout the building, and thermostat installations in walls. Additionally, these zoning systems typically include an expensive and difficult installation of a bypass damper system which is used to relieve excess static duct pressure.
Excess static duct pressure may result when a large number of the dampers restrict the air flow to the zones. In one implementation of a bypass damper system, a bypass damper is connected between the supply and return air duct. An airflow sensor is disposed in the supply air duct and is connected to the bypass damper. A bypass controller is also connected to the bypass damper and is used to modulate the bypass damper in response to the airflow measured by the airflow sensor. Thus, if the bypass controller determines that the air flow to the supply air duct causes excess static duct pressure then the bypass damper will be used to recycle the conditioned air to the return air duct. This implementation has the disadvantage of being expensive and difficult to install. Additionally, recycling the conditioned air can cause the HVAC system to overload. For example, if the HVAC system is set in heat mode and the bypass damper is activated to relieve excess pressure in the duct, the recycled heated air may continue to increase in temperature, as it recycles, which may cause a limit switch to shut down the HVAC system. Elimination of the aforementioned bypass damper system would reduce the amount of HVAC system equipment which in turn would reduce installation and maintenance costs.
Another implementation of a bypass damper system is similar to the bypass system mentioned above with the exception that the conditioned air is redirected to a dump, such as an equipment room, instead of being recycled to the intake duct. This implementation has the additional disadvantage of lost efficiency because the energy used to condition the redirected conditioned air is wasted.